The men who narrate Haruki Murakami's novels repeatedly claim to be utterly ordinary. They live blameless lives, keep their heads down, indulge moderately in jazz and beer, hope things will stay the same. And yet something happens: the ordinary man is catapulted into deranged circumstances. He might be forced to hunt down an evil sheep that wants to take over the world, or to investigate his wife's spectral disappearance.

Norwegian Wood, first published in Japan 13 years ago but only now translated for a western audience, might therefore puzzle the reader who has grown to love Murakami's haunting, melancholy surrealism: its action is resolutely realistic. And yet the narrator, Toru Watanabe, is just as baffled by life. At one point he writes: "I have never lied to anyone, and I have taken care over the years not to hurt other people. And yet I find myself tossed into this labyrinth." There is no moral justice in Murakami's world; there is only the duty - both epistemological and moral - to try to understand.

This duty also informs his first non-fiction volume, Underground. Murakami became obsessed with the 1995 Tokyo subway attack, in which Aum cult members released Sarin nerve gas on five separate trains. The book consists largely of edited transcripts of interviews conducted with survivors or relatives of victims. "How on earth did this happen to us?" one woman asks. "That 'How on earth...?' ", Murakami comments, "stuck in my head like a big question mark." No wonder: it is also the cry of pain that fires the depths of his fiction.

Norwegian Wood is a love story. The Beatles song of the title, heard by the 37-year-old Toru Watanabe, is an aural Proustian madeleine that transports him back to his student days. Watanabe has started at university in Tokyo the year after his best friend, Kizuki, killed himself. Kizuki's girlfriend Naoko and Watanabe have grown romantically close since their friend's death, but their love is complicated by Naoko's depression. Naoko enrols at a sanatorium, and the lonely Watanabe meets another woman, the flirtatiously vulnerable Midori. Thus is his "labyrinth" woven: a choice between idealised love and eternally sworn loyalty or flesh-and-blood happiness in the present.

The first chapter dreamily foreshadows the entire novel. Watanabe and Naoko, in the saturated colours and hyperreal detail of burned-in memory, are walking in a field, and Naoko playfully relates the local legend of the field well. No one knows where it is, and there is no encircling wall. You could fall down it at any time, and you would never get out.

Finding oneself down a well, or otherwise underground, is an oddly charged possibility in Murakami. The well can furnish a kind of metaphysical holiday - the narrator of Murakami's masterpiece to date, The Wind-Up Bird Chronicle, seeks out a well bottom in order to "think about reality". Alternatively, as Naoko fears in Norwegian Wood, being down a well might mean suffering in despair, being swallowed up by madness, inexorably dying. The horror of the Tokyo subway shares this motif with Murakami's fiction: as one survivor tells him: "The fear of going underground in a metal box and something bad happening is overpowering."

Norwegian Wood, simply told on the surface, slowly reveals its own subterranean currents. Chatting to Midori's dying father in hospital, for example, Watanabe mentions that he prefers Sophocles to Euripides. The implication is that conflicts will not be solved by an interfering deus ex machina, but can only unravel in tragic violence. Subtle allusions to Thomas Mann and The Great Gatsby contribute further eddies.

Such is the exquisite, gossamer construction of Murakami's writing that everything he chooses to describe trembles with symbolic possibility: a shirt on a washing-line, a string of paper cut-outs, a butterfly hairslide. Three times in the novel Watanabe reaches out to clutch light: first a sparkling mote of dust, next a firefly disappearing into the night. The third time he is strolling in the sanatorium gardens and becomes transfixed by Naoko's lit window in the distance, "like the final pulse of a soul's dying embers". You cannot retain the fleeting after-image of a firefly - similarly, perhaps, you cannot keep such embers alight by force of will. Maybe this bird, as John Lennon sang, has flown.

For all its metaphysical gloom, however, Norwegian Wood also flutters with sympathetic comedy. What on first glance appear to be bathetic lapses into jovial innuendo or irrelevant cookery chat between characters make the point that people in real life do not react to alarming or tragic situations in consistent or appropriate ways. Underground 's testimonies reflect the same truth - some survivors are angry, some scared, others calm or even lighthearted.

Underground is largely made up of the voices of others because, as a novelist, Murakami is "less interested in the 'big picture', as it were, than in the concrete, irreducible humanity of each individual". Norwegian Wood glows with this same interest, as its injured but hopeful characters hungrily seek happiness in odd places. Amazed by the overdubbed slurping and sucking of a porn-cinema soundtrack, Watanabe muses: "I felt strangely moved to think that I was living out my life on this bizarre planet of ours." The novel comes in two volumes, and just as the second jacket replaces blood red with spring green, so the ending is one of heavily battered, qualified optimism.

The Aum attack, meanwhile, eventually seems to Murakami to pose a challenge that is explicitly novelistic. Shoko Asahara, the cult leader, must have been a "master storyteller" in order to seduce so many intelligent individuals to his seemingly crazed version of Buddhism. In Murakami's view, the worst response to the massacre would be to view it as an aberration, a one-off evil perpetrated by spaced-out psychos. For his imaginative sympathy extends to the cult members, interviewed in the latter third of Underground, as well as to its victims.

Through Murakami's sensitive yet relentless questioning, it emerges that the people who joined Aum felt just as adrift in the world as Murakami's own characters do. One hyper-rational member describes his youthful frustration: "I couldn't find a single person who wanted to talk about the things that I cared about." But when he met Asahara, "It was like he saw the real me at a glance." In Murakami's fiction, too, people are tempted by eccentric, comforting myths: Naoko in Norwegian Wood becomes obsessed by the idea of a posthumous reunion with her first boyfriend; in the searingly brilliant A Wild Sheep Chase (also now published by Harvill), the megalomaniac ovine seduces its most powerful servant with a narrative: a malign logic that seems preferable to the impotent mess of daily life.

So before we dismiss the Aum cult as "utter nonsense", Murakami argues in Underground, we'd better make sure we have a narrative that is "potent" enough to chase it away. "It's something I'm going to have to deal with much more seriously from here on," he writes. As a statement of intent from a man who must already rank among the world's greatest living novelists, this is nothing less than thrilling.